/**
 * @file
 * This is the IPv4 layer implementation for incoming and outgoing IP traffic.
 *
 * @see ip_frag.c
 *
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 *
 */

#include "lwip/opt.h"
#include "lwip/ip.h"
#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/ip_frag.h"
#include "lwip/inet.h"
#include "lwip/inet_chksum.h"
#include "lwip/netif.h"
#include "lwip/icmp.h"
#include "lwip/igmp.h"
#include "lwip/raw.h"
#include "lwip/udp.h"
#include "lwip/tcp.h"
#include "lwip/snmp.h"
#include "lwip/dhcp.h"
#include "lwip/stats.h"
#include "arch/perf.h"

#include <string.h>

/**
 * The interface that provided the packet for the current callback
 * invocation.
 */
struct netif *current_netif;

/**
 * Header of the input packet currently being processed.
 */
const struct ip_hdr *current_header;

/**
 * Finds the appropriate network interface for a given IP address. It
 * searches the list of network interfaces linearly. A match is found
 * if the masked IP address of the network interface equals the masked
 * IP address given to the function.
 *
 * @param dest the destination IP address for which to find the route
 * @return the netif on which to send to reach dest
 */
struct netif *
ip_route(struct ip_addr *dest)
{
    struct netif *netif;

    /* iterate through netifs */
    for (netif = netif_list; netif != NULL; netif = netif->next)
    {
        /* network mask matches? */
        if (netif_is_up(netif))
        {
            if (ip_addr_netcmp(dest, &(netif->ip_addr), &(netif->netmask)))
            {
                /* return netif on which to forward IP packet */
                return netif;
            }
        }
    }
    if ((netif_default == NULL) || (!netif_is_up(netif_default)))
    {
        LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_route: No route to 0x%"X 32_F "\n", dest->addr));
        IP_STATS_INC(ip.rterr);
        snmp_inc_ipoutnoroutes();
        return NULL;
    }
    /* no matching netif found, use default netif */
    return netif_default;
}

#if IP_FORWARD
/**
 * Forwards an IP packet. It finds an appropriate route for the
 * packet, decrements the TTL value of the packet, adjusts the
 * checksum and outputs the packet on the appropriate interface.
 *
 * @param p the packet to forward (p->payload points to IP header)
 * @param iphdr the IP header of the input packet
 * @param inp the netif on which this packet was received
 * @return the netif on which the packet was sent (NULL if it wasn't sent)
 */
static struct netif *
ip_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp)
{
    struct netif *netif;

    PERF_START;
    /* Find network interface where to forward this IP packet to. */
    netif = ip_route((struct ip_addr*)&(iphdr->dest));
    if (netif == NULL)
    {
        LWIP_DEBUGF(IP_DEBUG, ("ip_forward: no forwarding route for 0x%"X 32_F " found\n",
                               iphdr->dest.addr));
        snmp_inc_ipoutnoroutes();
        return (struct netif*)NULL;
    }
    /* Do not forward packets onto the same network interface on which
     * they arrived. */
    if (netif == inp)
    {
        LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not bouncing packets back on incoming interface.\n"));
        snmp_inc_ipoutnoroutes();
        return (struct netif*)NULL;
    }

    /* decrement TTL */
    IPH_TTL_SET(iphdr, IPH_TTL(iphdr) - 1);
    /* send ICMP if TTL == 0 */
    if (IPH_TTL(iphdr) == 0)
    {
        snmp_inc_ipinhdrerrors();
#if LWIP_ICMP
        /* Don't send ICMP messages in response to ICMP messages */
        if (IPH_PROTO(iphdr) != IP_PROTO_ICMP)
        {
            icmp_time_exceeded(p, ICMP_TE_TTL);
        }
#endif  /* LWIP_ICMP */
        return (struct netif*)NULL;
    }

    /* Incrementally update the IP checksum. */
    if (IPH_CHKSUM(iphdr) >= htons(0xffff - 0x100))
    {
        IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100) + 1);
    }
    else
    {
        IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100));
    }

    LWIP_DEBUGF(IP_DEBUG, ("ip_forward: forwarding packet to 0x%"X 32_F "\n",
                           iphdr->dest.addr));

    IP_STATS_INC(ip.fw);
    IP_STATS_INC(ip.xmit);
    snmp_inc_ipforwdatagrams();

    PERF_STOP("ip_forward");
    /* transmit pbuf on chosen interface */
    netif->output(netif, p, (struct ip_addr*)&(iphdr->dest));
    return netif;
}
#endif /* IP_FORWARD */

/**
 * This function is called by the network interface device driver when
 * an IP packet is received. The function does the basic checks of the
 * IP header such as packet size being at least larger than the header
 * size etc. If the packet was not destined for us, the packet is
 * forwarded (using ip_forward). The IP checksum is always checked.
 *
 * Finally, the packet is sent to the upper layer protocol input function.
 *
 * @param p the received IP packet (p->payload points to IP header)
 * @param inp the netif on which this packet was received
 * @return ERR_OK if the packet was processed (could return ERR_* if it wasn't
 *         processed, but currently always returns ERR_OK)
 */
err_t
ip_input(struct pbuf *p, struct netif *inp)
{
    struct ip_hdr *iphdr;
    struct netif *netif;
    u16_t iphdr_hlen;
    u16_t iphdr_len;

#if LWIP_DHCP
    int check_ip_src = 1;
#endif /* LWIP_DHCP */

    IP_STATS_INC(ip.recv);
    snmp_inc_ipinreceives();

    /* identify the IP header */
    iphdr = p->payload;
    if (IPH_V(iphdr) != 4)
    {
        LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_WARNING, ("IP packet dropped due to bad version number %"U 16_F "\n", IPH_V(iphdr)));
        ip_debug_print(p);
        pbuf_free(p);
        IP_STATS_INC(ip.err);
        IP_STATS_INC(ip.drop);
        snmp_inc_ipinhdrerrors();
        return ERR_OK;
    }

    /* obtain IP header length in number of 32-bit words */
    iphdr_hlen = IPH_HL(iphdr);
    /* calculate IP header length in bytes */
    iphdr_hlen *= 4;
    /* obtain ip length in bytes */
    iphdr_len = ntohs(IPH_LEN(iphdr));

    /* header length exceeds first pbuf length, or ip length exceeds total pbuf length? */
    if ((iphdr_hlen > p->len) || (iphdr_len > p->tot_len))
    {
        if (iphdr_hlen > p->len)
        {
            LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
                        ("IP header (len %"U 16_F ") does not fit in first pbuf (len %"U 16_F "), IP packet dropped.\n",
                         iphdr_hlen, p->len));
        }
        if (iphdr_len > p->tot_len)
        {
            LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
                        ("IP (len %"U 16_F ") is longer than pbuf (len %"U 16_F "), IP packet dropped.\n",
                         iphdr_len, p->tot_len));
        }
        /* free (drop) packet pbufs */
        pbuf_free(p);
        IP_STATS_INC(ip.lenerr);
        IP_STATS_INC(ip.drop);
        snmp_inc_ipindiscards();
        return ERR_OK;
    }

    /* verify checksum */
#if CHECKSUM_CHECK_IP
    if (inet_chksum(iphdr, iphdr_hlen) != 0)
    {

        LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
                    ("Checksum (0x%"X 16_F ") failed, IP packet dropped.\n", inet_chksum(iphdr, iphdr_hlen)));
        ip_debug_print(p);
        pbuf_free(p);
        IP_STATS_INC(ip.chkerr);
        IP_STATS_INC(ip.drop);
        snmp_inc_ipinhdrerrors();
        return ERR_OK;
    }
#endif

    /* Trim pbuf. This should have been done at the netif layer,
     * but we'll do it anyway just to be sure that its done. */
    pbuf_realloc(p, iphdr_len);

    /* match packet against an interface, i.e. is this packet for us? */
#if LWIP_IGMP
    if (ip_addr_ismulticast(&(iphdr->dest)))
    {
        if ((inp->flags & NETIF_FLAG_IGMP) && (igmp_lookfor_group(inp, &(iphdr->dest))))
        {
            netif = inp;
        }
        else
        {
            netif = NULL;
        }
    }
    else
#endif /* LWIP_IGMP */
    {
        /* start trying with inp. if that's not acceptable, start walking the
           list of configured netifs.
           'first' is used as a boolean to mark whether we started walking the list */
        int first = 1;
        netif = inp;
        do
        {
            LWIP_DEBUGF(IP_DEBUG, ("ip_input: iphdr->dest 0x%"X 32_F " netif->ip_addr 0x%"X 32_F " (0x%"X 32_F ", 0x%"X 32_F ", 0x%"X 32_F ")\n",
                                   iphdr->dest.addr, netif->ip_addr.addr,
                                   iphdr->dest.addr & netif->netmask.addr,
                                   netif->ip_addr.addr & netif->netmask.addr,
                                   iphdr->dest.addr & ~(netif->netmask.addr)));

            /* interface is up and configured? */
            if ((netif_is_up(netif)) && (!ip_addr_isany(&(netif->ip_addr))))
            {
                /* unicast to this interface address? */
                if (ip_addr_cmp(&(iphdr->dest), &(netif->ip_addr)) ||
                    /* or broadcast on this interface network address? */
                    ip_addr_isbroadcast(&(iphdr->dest), netif))
                {
                    LWIP_DEBUGF(IP_DEBUG, ("ip_input: packet accepted on interface %c%c\n",
                                           netif->name[0], netif->name[1]));
                    /* break out of for loop */
                    break;
                }
            }
            if (first)
            {
                first = 0;
                netif = netif_list;
            }
            else
            {
                netif = netif->next;
            }
            if (netif == inp)
            {
                netif = netif->next;
            }
        }
        while (netif != NULL);
    }

#if LWIP_DHCP
    /* Pass DHCP messages regardless of destination address. DHCP traffic is addressed
     * using link layer addressing (such as Ethernet MAC) so we must not filter on IP.
     * According to RFC 1542 section 3.1.1, referred by RFC 2131).
     */
    if (netif == NULL)
    {
        /* remote port is DHCP server? */
        if (IPH_PROTO(iphdr) == IP_PROTO_UDP)
        {
            LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: UDP packet to DHCP client port %"U 16_F "\n",
                                                    ntohs(((struct udp_hdr*)((u8_t*)iphdr + iphdr_hlen))->dest)));
            if (ntohs(((struct udp_hdr*)((u8_t*)iphdr + iphdr_hlen))->dest) == DHCP_CLIENT_PORT)
            {
                LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: DHCP packet accepted.\n"));
                netif = inp;
                check_ip_src = 0;
            }
        }
    }
#endif /* LWIP_DHCP */

    /* broadcast or multicast packet source address? Compliant with RFC 1122: 3.2.1.3 */
#if LWIP_DHCP
    /* DHCP servers need 0.0.0.0 to be allowed as source address (RFC 1.1.2.2: 3.2.1.3/a) */
    if (check_ip_src && (iphdr->src.addr != 0))
#endif /* LWIP_DHCP */
    {  if ((ip_addr_isbroadcast(&(iphdr->src), inp)) ||
           (ip_addr_ismulticast(&(iphdr->src))))
       {
           /* packet source is not valid */
           LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("ip_input: packet source is not valid.\n"));
           /* free (drop) packet pbufs */
           pbuf_free(p);
           IP_STATS_INC(ip.drop);
           snmp_inc_ipinaddrerrors();
           snmp_inc_ipindiscards();
           return ERR_OK;
       }
    }

    /* packet not for us? */
    if (netif == NULL)
    {
        /* packet not for us, route or discard */
        LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_TRACE, ("ip_input: packet not for us.\n"));
#if IP_FORWARD
        /* non-broadcast packet? */
        if (!ip_addr_isbroadcast(&(iphdr->dest), inp))
        {
            /* try to forward IP packet on (other) interfaces */
            ip_forward(p, iphdr, inp);
        }
        else
#endif  /* IP_FORWARD */
        {
            snmp_inc_ipinaddrerrors();
            snmp_inc_ipindiscards();
        }
        pbuf_free(p);
        return ERR_OK;
    }
    /* packet consists of multiple fragments? */
    if ((IPH_OFFSET(iphdr) & htons(IP_OFFMASK | IP_MF)) != 0)
    {
#if IP_REASSEMBLY /* packet fragment reassembly code present? */
        LWIP_DEBUGF(IP_DEBUG, ("IP packet is a fragment (id=0x%04"X 16_F " tot_len=%"U 16_F " len=%"U 16_F " MF=%"U 16_F " offset=%"U 16_F "), calling ip_reass()\n",
                               ntohs(IPH_ID(iphdr)), p->tot_len, ntohs(IPH_LEN(iphdr)), !!(IPH_OFFSET(iphdr) & htons(IP_MF)), (ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK) * 8));
        /* reassemble the packet*/
        p = ip_reass(p);
        /* packet not fully reassembled yet? */
        if (p == NULL)
        {
            return ERR_OK;
        }
        iphdr = p->payload;
#else   /* IP_REASSEMBLY == 0, no packet fragment reassembly code present */
        pbuf_free(p);
        LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("IP packet dropped since it was fragmented (0x%"X 16_F ") (while IP_REASSEMBLY == 0).\n",
                                                        ntohs(IPH_OFFSET(iphdr))));
        IP_STATS_INC(ip.opterr);
        IP_STATS_INC(ip.drop);
        /* unsupported protocol feature */
        snmp_inc_ipinunknownprotos();
        return ERR_OK;
#endif  /* IP_REASSEMBLY */
    }

#if IP_OPTIONS_ALLOWED == 0 /* no support for IP options in the IP header? */

#if LWIP_IGMP
    /* there is an extra "router alert" option in IGMP messages which we allow for but do not police */
    if ((iphdr_hlen > IP_HLEN &&  (IPH_PROTO(iphdr) != IP_PROTO_IGMP)) {
#else
    if (iphdr_hlen > IP_HLEN)
    {
#endif  /* LWIP_IGMP */
            LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("IP packet dropped since there were IP options (while IP_OPTIONS_ALLOWED == 0).\n"));
            pbuf_free(p);
            IP_STATS_INC(ip.opterr);
            IP_STATS_INC(ip.drop);
            /* unsupported protocol feature */
            snmp_inc_ipinunknownprotos();
            return ERR_OK;
        }
#endif /* IP_OPTIONS_ALLOWED == 0 */

    /* send to upper layers */
    LWIP_DEBUGF(IP_DEBUG, ("ip_input: \n"));
    ip_debug_print(p);
    LWIP_DEBUGF(IP_DEBUG, ("ip_input: p->len %"U 16_F " p->tot_len %"U 16_F "\n", p->len, p->tot_len));

    current_netif = inp;
    current_header = iphdr;

#if LWIP_RAW
    /* raw input did not eat the packet? */
    if (raw_input(p, inp) == 0)
#endif /* LWIP_RAW */
    {

        switch (IPH_PROTO(iphdr))
        {
#if LWIP_UDP
        case IP_PROTO_UDP:
#if LWIP_UDPLITE
        case IP_PROTO_UDPLITE:
#endif      /* LWIP_UDPLITE */
            snmp_inc_ipindelivers();
            udp_input(p, inp);
            break;
#endif      /* LWIP_UDP */
#if LWIP_TCP
        case IP_PROTO_TCP:
            snmp_inc_ipindelivers();
            tcp_input(p, inp);
            break;
#endif      /* LWIP_TCP */
#if LWIP_ICMP
        case IP_PROTO_ICMP:
            snmp_inc_ipindelivers();
            icmp_input(p, inp);
            break;
#endif      /* LWIP_ICMP */
#if LWIP_IGMP
        case IP_PROTO_IGMP:
            igmp_input(p, inp, &(iphdr->dest));
            break;
#endif      /* LWIP_IGMP */
        default:
#if LWIP_ICMP
            /* send ICMP destination protocol unreachable unless is was a broadcast */
            if (!ip_addr_isbroadcast(&(iphdr->dest), inp) &&
                !ip_addr_ismulticast(&(iphdr->dest)))
            {
                p->payload = iphdr;
                icmp_dest_unreach(p, ICMP_DUR_PROTO);
            }
#endif      /* LWIP_ICMP */
            pbuf_free(p);

            LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("Unsupported transport protocol %"U 16_F "\n", IPH_PROTO(iphdr)));

            IP_STATS_INC(ip.proterr);
            IP_STATS_INC(ip.drop);
            snmp_inc_ipinunknownprotos();
        }
    }

    current_netif = NULL;
    current_header = NULL;

    return ERR_OK;
}

/**
 * Sends an IP packet on a network interface. This function constructs
 * the IP header and calculates the IP header checksum. If the source
 * IP address is NULL, the IP address of the outgoing network
 * interface is filled in as source address.
 * If the destination IP address is IP_HDRINCL, p is assumed to already
 * include an IP header and p->payload points to it instead of the data.
 *
 * @param p the packet to send (p->payload points to the data, e.g. next
            protocol header; if dest == IP_HDRINCL, p already includes an IP
            header and p->payload points to that IP header)
 * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
 *         IP  address of the netif used to send is used as source address)
 * @param dest the destination IP address to send the packet to
 * @param ttl the TTL value to be set in the IP header
 * @param tos the TOS value to be set in the IP header
 * @param proto the PROTOCOL to be set in the IP header
 * @param netif the netif on which to send this packet
 * @return ERR_OK if the packet was sent OK
 *         ERR_BUF if p doesn't have enough space for IP/LINK headers
 *         returns errors returned by netif->output
 *
 * @note ip_id: RFC791 "some host may be able to simply use
 *  unique identifiers independent of destination"
 */
err_t
ip_output_if(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
             u8_t ttl, u8_t tos,
             u8_t proto, struct netif *netif)
{
#if IP_OPTIONS_SEND
    return ip_output_if_opt(p, src, dest, ttl, tos, proto, netif, NULL, 0);
}

/**
 * Same as ip_output_if() but with the possibility to include IP options:
 *
 * @ param ip_options pointer to the IP options, copied into the IP header
 * @ param optlen length of ip_options
 */
err_t ip_output_if_opt(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
                       u8_t ttl, u8_t tos, u8_t proto, struct netif *netif, void *ip_options,
                       u16_t optlen)
{
#endif /* IP_OPTIONS_SEND */
    struct ip_hdr *iphdr;
    static u16_t ip_id = 0;

    snmp_inc_ipoutrequests();

    /* Should the IP header be generated or is it already included in p? */
    if (dest != IP_HDRINCL)
    {
        u16_t ip_hlen = IP_HLEN;
#if IP_OPTIONS_SEND
        u16_t optlen_aligned = 0;
        if (optlen != 0)
        {
            /* round up to a multiple of 4 */
            optlen_aligned = ((optlen + 3) & ~3);
            ip_hlen += optlen_aligned;
            /* First write in the IP options */
            if (pbuf_header(p, optlen_aligned))
            {
                LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_output_if_opt: not enough room for IP options in pbuf\n"));
                IP_STATS_INC(ip.err);
                snmp_inc_ipoutdiscards();
                return ERR_BUF;
            }
            MEMCPY(p->payload, ip_options, optlen);
            if (optlen < optlen_aligned)
            {
                /* zero the remaining bytes */
                memset(((char*)p->payload) + optlen, 0, optlen_aligned - optlen);
            }
        }
#endif  /* IP_OPTIONS_SEND */
        /* generate IP header */
        if (pbuf_header(p, IP_HLEN))
        {
            LWIP_DEBUGF(IP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("ip_output: not enough room for IP header in pbuf\n"));

            IP_STATS_INC(ip.err);
            snmp_inc_ipoutdiscards();
            return ERR_BUF;
        }

        iphdr = p->payload;
        LWIP_ASSERT("check that first pbuf can hold struct ip_hdr",
                    (p->len >= sizeof(struct ip_hdr)));

        IPH_TTL_SET(iphdr, ttl);
        IPH_PROTO_SET(iphdr, proto);

        ip_addr_set(&(iphdr->dest), dest);

        IPH_VHLTOS_SET(iphdr, 4, ip_hlen / 4, tos);
        IPH_LEN_SET(iphdr, htons(p->tot_len));
        IPH_OFFSET_SET(iphdr, 0);
        IPH_ID_SET(iphdr, htons(ip_id));
        ++ip_id;

        if (ip_addr_isany(src))
        {
            ip_addr_set(&(iphdr->src), &(netif->ip_addr));
        }
        else
        {
            ip_addr_set(&(iphdr->src), src);
        }

        IPH_CHKSUM_SET(iphdr, 0);
#if CHECKSUM_GEN_IP
        IPH_CHKSUM_SET(iphdr, inet_chksum(iphdr, ip_hlen));
#endif
    }
    else
    {
        /* IP header already included in p */
        iphdr = p->payload;
        dest = &(iphdr->dest);
    }

    IP_STATS_INC(ip.xmit);

    LWIP_DEBUGF(IP_DEBUG, ("ip_output_if: %c%c%"U 16_F "\n", netif->name[0], netif->name[1], netif->num));
    ip_debug_print(p);

#if ENABLE_LOOPBACK
    if (ip_addr_cmp(dest, &netif->ip_addr))
    {
        /* Packet to self, enqueue it for loopback */
        LWIP_DEBUGF(IP_DEBUG, ("netif_loop_output()"));
        return netif_loop_output(netif, p, dest);
    }
#endif /* ENABLE_LOOPBACK */
#if IP_FRAG
    /* don't fragment if interface has mtu set to 0 [loopif] */
    if (netif->mtu && (p->tot_len > netif->mtu))
    {
        return ip_frag(p, netif, dest);
    }
#endif

    LWIP_DEBUGF(IP_DEBUG, ("netif->output()"));
    return netif->output(netif, p, dest);
}

/**
 * Simple interface to ip_output_if. It finds the outgoing network
 * interface and calls upon ip_output_if to do the actual work.
 *
 * @param p the packet to send (p->payload points to the data, e.g. next
            protocol header; if dest == IP_HDRINCL, p already includes an IP
            header and p->payload points to that IP header)
 * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
 *         IP  address of the netif used to send is used as source address)
 * @param dest the destination IP address to send the packet to
 * @param ttl the TTL value to be set in the IP header
 * @param tos the TOS value to be set in the IP header
 * @param proto the PROTOCOL to be set in the IP header
 *
 * @return ERR_RTE if no route is found
 *         see ip_output_if() for more return values
 */
err_t
ip_output(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
          u8_t ttl, u8_t tos, u8_t proto)
{
    struct netif *netif;

    if ((netif = ip_route(dest)) == NULL)
    {
        LWIP_DEBUGF(IP_DEBUG, ("ip_output: No route to 0x%"X 32_F "\n", dest->addr));
        IP_STATS_INC(ip.rterr);
        return ERR_RTE;
    }

    return ip_output_if(p, src, dest, ttl, tos, proto, netif);
}

#if LWIP_NETIF_HWADDRHINT
/** Like ip_output, but takes and addr_hint pointer that is passed on to netif->addr_hint
 *  before calling ip_output_if.
 *
 * @param p the packet to send (p->payload points to the data, e.g. next
            protocol header; if dest == IP_HDRINCL, p already includes an IP
            header and p->payload points to that IP header)
 * @param src the source IP address to send from (if src == IP_ADDR_ANY, the
 *         IP  address of the netif used to send is used as source address)
 * @param dest the destination IP address to send the packet to
 * @param ttl the TTL value to be set in the IP header
 * @param tos the TOS value to be set in the IP header
 * @param proto the PROTOCOL to be set in the IP header
 * @param addr_hint address hint pointer set to netif->addr_hint before
 *        calling ip_output_if()
 *
 * @return ERR_RTE if no route is found
 *         see ip_output_if() for more return values
 */
err_t
ip_output_hinted(struct pbuf *p, struct ip_addr *src, struct ip_addr *dest,
                 u8_t ttl, u8_t tos, u8_t proto, u8_t *addr_hint)
{
    struct netif *netif;
    err_t err;

    if ((netif = ip_route(dest)) == NULL)
    {
        LWIP_DEBUGF(IP_DEBUG, ("ip_output: No route to 0x%"X 32_F "\n", dest->addr));
        IP_STATS_INC(ip.rterr);
        return ERR_RTE;
    }

    netif->addr_hint = addr_hint;
    err = ip_output_if(p, src, dest, ttl, tos, proto, netif);
    netif->addr_hint = NULL;

    return err;
}
#endif /* LWIP_NETIF_HWADDRHINT*/

#if IP_DEBUG
/* Print an IP header by using LWIP_DEBUGF
 * @param p an IP packet, p->payload pointing to the IP header
 */
void
ip_debug_print(struct pbuf *p)
{
    struct ip_hdr *iphdr = p->payload;
    u8_t *payload;

    payload = (u8_t*)iphdr + IP_HLEN;

    LWIP_DEBUGF(IP_DEBUG, ("IP header:\n"));
    LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(IP_DEBUG, ("|%2"S 16_F " |%2"S 16_F " |  0x%02"X 16_F " |     %5"U 16_F "     | (v, hl, tos, len)\n",
                           IPH_V(iphdr),
                           IPH_HL(iphdr),
                           IPH_TOS(iphdr),
                           ntohs(IPH_LEN(iphdr))));
    LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(IP_DEBUG, ("|    %5"U 16_F "      |%"U 16_F "%"U 16_F "%"U 16_F "|    %4"U 16_F "   | (id, flags, offset)\n",
                           ntohs(IPH_ID(iphdr)),
                           ntohs(IPH_OFFSET(iphdr)) >> 15 & 1,
                           ntohs(IPH_OFFSET(iphdr)) >> 14 & 1,
                           ntohs(IPH_OFFSET(iphdr)) >> 13 & 1,
                           ntohs(IPH_OFFSET(iphdr)) & IP_OFFMASK));
    LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(IP_DEBUG, ("|  %3"U 16_F "  |  %3"U 16_F "  |    0x%04"X 16_F "     | (ttl, proto, chksum)\n",
                           IPH_TTL(iphdr),
                           IPH_PROTO(iphdr),
                           ntohs(IPH_CHKSUM(iphdr))));
    LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(IP_DEBUG, ("|  %3"U 16_F "  |  %3"U 16_F "  |  %3"U 16_F "  |  %3"U 16_F "  | (src)\n",
                           ip4_addr1(&iphdr->src),
                           ip4_addr2(&iphdr->src),
                           ip4_addr3(&iphdr->src),
                           ip4_addr4(&iphdr->src)));
    LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(IP_DEBUG, ("|  %3"U 16_F "  |  %3"U 16_F "  |  %3"U 16_F "  |  %3"U 16_F "  | (dest)\n",
                           ip4_addr1(&iphdr->dest),
                           ip4_addr2(&iphdr->dest),
                           ip4_addr3(&iphdr->dest),
                           ip4_addr4(&iphdr->dest)));
    LWIP_DEBUGF(IP_DEBUG, ("+-------------------------------+\n"));
}
#endif /* IP_DEBUG */
